1. Field of the Invention
The present invention relates to the field of display technology and, more particularly, to a level shift circuit, a liquid crystal display device and a charge sharing method.
2. Description of Related Art
Because of advantages such as light weight, thin thickness, low radiation, etc., the liquid crystal display device has gradually replaced the CRT display device (i.e., the cathode ray tube display device) and becomes a main stream of fabricating the PC monitor (i.e., the display of the computer) and the TV set (i.e., the television set). The liquid crystal display device typically comprises a display panel, a circuit board, a gate driving circuit and a source driving circuit, wherein the gate driving circuit and the source driving circuit are disposed on the display panel. In addition, a timing controller is disposed on the circuit board and is configured for providing a plurality of control signals to the gate driving circuit and the source driving circuit. The gate driving circuit is configured for driving a plurality of gate lines on the display panel, and the source driving circuit is configured for outputting image signal to a plurality of data lines which are across the gate lines on the display panel. The gate driving circuit and the source driving circuit can be disposed on the display panel in a TCP form (i.e., tape carrier packaging form) or a COG form (i.e., chip on glass form). Furthermore, the gate driving circuit can be directly formed in the display panel, and this is so called GOA circuit (i.e., gate-on-array circuit). The structure which directly forms the gate driving circuit in the display panel comprises the shift register. The shift register comprises a plurality of stages which are connected in cascade, and the stages are configured for generating a plurality of gate driving pulses to drive the gate lines formed on the display panel sequentially.
In the current designs of the two phase GOA, the level shift circuit is disposed on the circuit board, so as to generate two clock pulse signals to sever as the clock pulse signals of the odd stage and the even stage respectively and to provide the energy needed by the gate driving pulses. Since the voltage amplitudes of the clock pulse signals (i.e., the voltage difference between the high level and the low level) are larger and more stages are coupled to the clock pulse signals, the parasitic capacitance is quite large. Keeping on charging and discharging the capacitance will result in power consumption, so that the charge sharing is needed to reduce the power consumption of the level shift circuit. Generally speaking, the polarities of the clock pulse signals are reverse. In current charge sharing methods, the clock pulse signals are coupled to each other to share charge to be pulled to a center voltage before the clock pulse signals change the polarities thereof. After that, the clock pulse signals are amplified to a target voltage by the output buffers of the level shift circuit respectively. Basically, the level shift circuit is just a simple amplifier and is incapable of performing the charge sharing function. Since the polarities of the clock pulse signals are reverse, one of the clock pulse signals should be pulled to low when the other one is pulled to high. That is, the clock pulse signals can not be pulled to the low level or the high level at the same time, resulting in the lack of the design flexibility of the waveforms.
On the other hand, for the designs of other multi-phase GOA (e.g. 4 phase GOA) and according to the current requirements of the waveforms, at least some of the time periods of the utilized multi-phase clock pulse signals situating in a high level overlap, so that the charge sharing can not be performed as the way adopted by the above-mentioned 2 phase clock pulses. This results in more power consumption. Furthermore, since the charge sharing can not be performed and the waveforms of the clock pulse signals are square waves, the feed-through effect is more serious, and this will affect the display quality of the display device.